A post-processing apparatus for post-processing a sheet carried from an image forming device (for example, an MFP) is known. The post-processing apparatus includes a processing unit for stapling or sorting the carried sheet. In addition, the post-processing apparatus includes a saddle folding unit that performs so-called saddle-folding, in which a plurality of sheets are bundled and folded in half. The saddle folding unit includes a blade capable of reciprocating so as to insert and remove a leading edge with respect to a nip portion of a pair of folding rollers. The blade enters a nip portion while pushing a central portion of a sheet into the nip portion between a pair of folding rollers.
However, in a case where the blade pushes the sheet into the nip portion, there is a possibility of slippage between the blade and the sheet. When undesired slippage occurs between the blade and the sheet, there is a possibility that the central portion of the sheet cannot be accurately pushed into the nip portion.